Hybrid block-based processor and custom function blocks

ABSTRACT

Apparatus and methods are disclosed for implementing block-based processors having custom function blocks, including field-programmable gate array (FPGA) implementations. In some examples of the disclosed technology, a dynamically configurable scheduler is configured to issue at least one block-based processor instruction. A custom function block is configured to receive input operands for the instruction and generate ready state data indicating completion of a computation performed for the instruction by the respective custom function block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/328,976, entitled “OUT-OF-ORDER BLOCK-BASED PROCESSORS AND INSTRUCTION SCHEDULERS,” filed Apr. 28, 2016, which is incorporated herein by reference in its entirety.

BACKGROUND

Microprocessors have benefitted from continuing gains in transistor count, integrated circuit cost, manufacturing capital, clock frequency, and energy efficiency due to continued transistor scaling predicted by Moore's law, with little change in associated processor Instruction Set Architectures (ISAs). However, the benefits realized from photolithographic scaling, which drove the semiconductor industry over the last 40 years, are slowing or even reversing. Reduced Instruction Set Computing (RISC) architectures have been the dominant paradigm in processor design for many years. Out-of-order superscalar implementations have not exhibited sustained improvement in area or performance. Accordingly, there is ample opportunity for improvements in processor ISAs to extend performance improvements.

SUMMARY

Methods, apparatus, and computer-readable storage devices are disclosed for configuring, operating, and compiling code for, block-based processor architectures (BB-ISAs), including explicit data graph execution (EDGE) architectures. The microarchitecture of the processors includes a parallel instruction scheduler. The described techniques and tools for solutions for, e.g., improving processor performance and/or reducing energy consumption can be implemented separately, or in various combinations with each other. As will be described more fully below, the described techniques and tools can be implemented in a digital signal processor, microprocessor, application-specific integrated circuit (ASIC), a soft processor (e.g., a microprocessor core implemented in a field programmable gate array (FPGA) using reconfigurable logic), programmable logic, or other suitable logic circuitry. As will be readily apparent to one of ordinary skill in the art, the disclosed technology can be implemented in various computing platforms, including, but not limited to, servers, mainframes, cellphones, smartphones, handheld devices, handheld computers, personal digital assistants (PDAs), touch screen tablet devices, tablet computers, wearable computers, and laptop computers.

Soft processor implementations of block-based processor architectures can improve design productivity. For example, descriptions of a block-based soft-processor written in a suitable description language (e.g., C, SystemC, SystemVerilog, or Verilog) can undergo logic synthesized to generate a gate-level netlist mapped to an FPGA. A bitstream is generated for the FPGA that is used to program the FPGA. A costly initial port of software into hardware instead becomes a simple cross-compile targeting the soft processors, and most design turns are quick recompiles. Application bottlenecks can then be offloaded to custom hardware exposed as new instructions, function units, autonomous accelerators, memories, or interconnects.

Certain examples of the disclosed technology allow for the configuration of high instruction level parallelism (ILP), out-of-order (OoO) superscalar soft processors without reduced complexity and overhead. In some examples, an Explicit Data Graph Execution (EDGE) instruction set architecture is provided for area and energy efficient high ILP execution. Together the EDGE architecture and its compiler finesse away much of the register renaming, CAMs, and complexity, enabling an out-of-order processor for only a few hundred FPGA lookup tables (“LUTs”) more than an in-order scalar RISC.

The disclosed technology can be used to add additional, arbitrary functional units to a processor. In some examples, a new functional unit is defined in RTL and compiled and mapped to an FPGA using development tools. In some examples, a processor is coupled to programmable logic that can be configured (once, a priori, or at runtime) to perform an arbitrary logic function. Through the use of the disclosed operand buffers, input operands to the new functional unit, and output operands from the new functional unit, can be scheduled by the processor just as any other built-in function.

This disclosed technology introduces an EDGE ISA and explores how EDGE microarchitectures compare to in-order RISCs. Methods and apparatus are disclosed for building small, fast dataflow instruction schedulers in FPGAs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example block-based processor including multiple processor cores as can be employed according to some examples of the disclosed technology.

FIG. 2 illustrates an example microarchitecture for implementing a block-based processor with custom function units, as can be used in certain examples of the disclosed technology.

FIG. 3 is a block diagram outlining an example FPGA microarchitecture as can be used in some examples of the disclosed technology.

FIG. 4 illustrates example reconfigurable logic in a reconfigurable logic block as can be used in certain examples of the disclosed technology.

FIG. 5 illustrates example block-based processor headers and instructions, as can be used in some examples of the disclosed technology.

FIG. 6 illustrates an example source code portion and corresponding instruction blocks, as can be used in certain examples of the disclosed technology.

FIG. 7 illustrates an example of instruction formats that can be used for certain examples of block-based processors in certain examples of the disclosed technology.

FIG. 8 is a flow chart illustrating an example of a progression of execution states of a processor core in a block-based processor, as can be used in certain examples of the disclosed technology.

FIG. 9 is a block diagram outlining an example microarchitecture including a custom function block, as can be implemented according to certain examples of the disclosed technologies.

FIG. 10 is a block diagram of a custom function block that can be used to execute fused instructions, according to certain examples of the disclosed technology.

FIG. 11 is a block diagram illustrating an example configuration including a block-based processor and memory, as can be used in certain examples of the disclosed technology.

FIG. 12 is a flowchart outlining and example method of executing instructions specifying custom function units, as can be performed in certain examples of the disclosed technology.

FIG. 13 is a flowchart illustrating an example method of executing fused instructions with a custom function unit, as can be performed in certain examples of the disclosed technology.

FIG. 14 is a flowchart outlining an example of using profile performance data for an instruction block to execute instructions with a custom function block, as can be performed in certain examples of the disclosed technology.

FIG. 15 is a flowchart outlining an example of producing a configuration bitstream for a block-based processor that includes custom function blocks, as can be performed in certain examples of the disclosed technology.

FIG. 16 is a block diagram illustrating a suitable computing environment for implementing certain embodiments of the disclosed technology.

DETAILED DESCRIPTION

I. General Considerations

This disclosure is set forth in the context of representative embodiments that are not intended to be limiting in any way.

As used in this application the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the term “coupled” encompasses mechanical, electrical, magnetic, optical, as well as other practical ways of coupling or linking items together, and does not exclude the presence of intermediate elements between the coupled items. Furthermore, as used herein, the term “and/or” means any one item or combination of items in the phrase.

The systems, methods, and apparatus described herein should not be construed as being limiting in any way. Instead, this disclosure is directed toward all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and apparatus are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed things and methods require that any one or more specific advantages be present or problems be solved. Furthermore, any features or aspects of the disclosed embodiments can be used in various combinations and subcombinations with one another.

Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed things and methods can be used in conjunction with other things and methods. Additionally, the description sometimes uses terms like “produce,” “generate,” “display,” “receive,” “emit,” “verify,” “execute,” and “initiate” to describe the disclosed methods. These terms are high-level descriptions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

Theories of operation, scientific principles, or other theoretical descriptions presented herein in reference to the apparatus or methods of this disclosure have been provided for the purposes of better understanding and are not intended to be limiting in scope. The apparatus and methods in the appended claims are not limited to those apparatus and methods that function in the manner described by such theories of operation.

Any of the disclosed methods can be implemented as computer-executable instructions stored on one or more computer-readable media (e.g., computer-readable media, such as one or more optical media discs, volatile memory components (such as DRAM or SRAM), or nonvolatile memory components (such as hard drives)) and executed on a computer (e.g., any commercially available computer, including smart phones or other mobile devices that include computing hardware). Any of the computer-executable instructions for implementing the disclosed techniques, as well as any data created and used during implementation of the disclosed embodiments, can be stored on one or more computer-readable media (e.g., computer-readable storage media). The computer-executable instructions can be part of, for example, a dedicated software application or a software application that is accessed or downloaded via a web browser or other software application (such as a remote computing application). Such software can be executed, for example, on a single local computer (e.g., with general-purpose and/or block-based processors executing on any suitable commercially available computer) or in a network environment (e.g., via the Internet, a wide-area network, a local-area network, a client-server network (such as a cloud computing network), or other such network) using one or more network computers.

For clarity, only certain selected aspects of the software-based implementations are described. Other details that are well known in the art are omitted. For example, it should be understood that the disclosed technology is not limited to any specific computer language or program. For instance, the disclosed technology can be implemented by software written in C, C++, Java, or any other suitable programming language. Likewise, the disclosed technology is not limited to any particular computer or type of hardware. Certain details of suitable computers and hardware are well-known and need not be set forth in detail in this disclosure.

Furthermore, any of the software-based embodiments (comprising, for example, computer-executable instructions for causing a computer to perform any of the disclosed methods) can be uploaded, downloaded, or remotely accessed through a suitable communication means. Such suitable communication means include, for example, the Internet, the World Wide Web, an intranet, software applications, cable (including fiber optic cable), magnetic communications, electromagnetic communications (including RF, microwave, and infrared communications), electronic communications, or other such communication means.

II. Introduction to the Disclosed Technologies

Superscalar out-of-order microarchitectures employ substantial circuit resources to rename registers, schedule instructions in dataflow order, clean up after miss-speculation, and retire results in-order for precise exceptions. This includes expensive circuits, such as deep, many-ported register files, many-ported content-accessible memories (CAMs) for dataflow instruction scheduling wakeup, and many-wide bus multiplexers and bypass networks, all of which are resource intensive. For example, FPGA-based implementations of multi-read, multi-write RAMs typically require a mix of replication, multi-cycle operation, clock doubling, bank interleaving, live-value tables, and other expensive techniques.

The disclosed technologies can realize performance enhancement through application of techniques including high instruction-level parallelism (ILP), out-of-order (OoO), superscalar execution, while avoiding substantial complexity and overhead in both processor hardware and associated software. In some examples of the disclosed technology, a block-based processor uses an EDGE ISA designed for area- and energy-efficient, high-ILP execution. In some examples, use of EDGE architectures and associated compilers finesses away much of the register renaming, CAMs, and complexity.

In certain examples of the disclosed technology, an EDGE ISA can eliminate the need for one or more complex architectural features, including register renaming, dataflow analysis, misspeculation recovery, and in-order retirement while supporting mainstream programming languages such as C and C++. In certain examples of the disclosed technology, a block-based processor executes a plurality of two or more instructions as an atomic block. Block-based instructions can be used to express semantics of program data flow and/or instruction flow in a more explicit fashion, allowing for improved compiler and processor performance. In certain examples of the disclosed technology, an explicit data graph execution instruction set architecture (EDGE ISA) includes information about program control flow that can be used to improve detection of improper control flow instructions, thereby increasing performance, saving memory resources, and/or and saving energy.

In some examples of the disclosed technology, instructions organized within instruction blocks are fetched, executed, and committed atomically. Instructions inside blocks execute in dataflow order, which reduces or eliminates using register renaming and provides power-efficient OoO execution. A compiler can be used to explicitly encode data dependencies through the ISA, reducing or eliminating burdening processor core control logic from rediscovering dependencies at runtime. Using predicated execution, intra-block branches can be converted to dataflow instructions, and dependencies, other than memory dependencies, can be limited to direct data dependencies. Disclosed target form encoding techniques allow instructions within a block to communicate their operands directly via operand buffers, reducing accesses to a power-hungry, multi-ported physical register files.

Between instruction blocks, instructions can communicate using memory and registers. Thus, by utilizing a hybrid dataflow execution model, EDGE architectures can still support imperative programming languages and sequential memory semantics, but desirably also enjoy the benefits of out-of-order execution with near in-order power efficiency and complexity.

III. Example Block-Based Processor

FIG. 1 is a block diagram 10 of a block-based processor 100 as can be implemented in some examples of the disclosed technology. The processor 100 is configured to execute atomic blocks of instructions according to an instruction set architecture (ISA), which describes a number of aspects of processor operation, including a register model, a number of defined operations performed by block-based instructions, a memory model, interrupts, and other architectural features. The block-based processor includes a plurality of one or more processing cores 110, including a processor core 111. The block-based processor can be implemented in as a custom or application-specific integrated circuit (e.g., including a system-on-chip (SoC) integrated circuit), as a field programmable gate array (FPGA) or other reconfigurable logic, or as a soft processor virtual machine hosted by a physical general purpose processor. The processor cores 110 can including one or more custom function blocks, as further detailed below. The custom function blocks are configured to provide custom functionality, such as functions not directly supported by block-based processor's ISA. In some examples, the custom function blocks are implemented with reconfigurable logic.

As shown in FIG. 1, the processor cores are connected to each other via core interconnect 120. The core interconnect 120 carries data and control signals between individual ones of the cores 110, a memory interface 140, and an input/output (I/O) interface 150. The core interconnect 120 can transmit and receive signals using electrical, optical, magnetic, or other suitable communication technology and can provide communication connections arranged according to a number of different topologies, depending on a particular desired configuration. For example, the core interconnect 120 can have a crossbar, a bus, a point-to-point bus, or other suitable topology. In some examples, any one of the cores 110 can be connected to any of the other cores, while in other examples, some cores are only connected to a subset of the other cores. For example, each core may only be connected to a nearest 4, 8, or 20 neighboring cores. The core interconnect 120 can be used to transmit input/output data to and from the cores, as well as transmit control signals and other information signals to and from the cores. For example, each of the cores 110 can receive and transmit semaphores that indicate the execution status of instructions currently being executed by each of the respective cores. In some examples, the core interconnect 120 is implemented as wires connecting the cores 110, and memory system, while in other examples, the core interconnect can include circuitry for multiplexing data signals on the interconnect wire(s), switch and/or routing components, including active signal drivers and repeaters, or other suitable circuitry. In some examples of the disclosed technology, signals transmitted within and to/from the processor 100 are not limited to full swing electrical digital signals, but the processor can be configured to include differential signals, pulsed signals, or other suitable signals for transmitting data and control signals.

In the example of FIG. 1, the memory interface 140 of the processor includes interface logic that is used to connect to memory 145, for example, memory located on another integrated circuit besides the processor 100 (e.g., the memory can be static RAM (SRAM) or dynamic RAM (DRAM)), or memory embedded on the same integrated circuit as the processor (e.g., embedded SRAM or DRAM (eDRAM)). The memory interface 140 and/or the main memory can include caches (e.g., n-way or associative caches) to improve memory access performance In some examples the cache is implemented using static RAM (SRAM) and the main memory 145 is implemented using dynamic RAM (DRAM). In some examples the memory interface 140 is included on the same integrated circuit as the other components of the processor 100. In some examples, the memory interface 140 includes a direct memory access (DMA) controller allowing transfer of blocks of data in memory without using register file(s) and/or the processor 100. In some examples, the memory interface 140 manages allocation of virtual memory, expanding the available main memory 145. In some examples, support for bypassing cache structures or for ensuring cache coherency when performing memory synchronization operations (e.g., handling contention issues or shared memory between plural different threads, processes, or processors) are provided by the memory interface 140 and/or respective cache structures. In some examples, a dynamically-generated partial reconfiguration bitstream for one or more custom functional blocks can be stored in the memory 145.

The I/O interface 150 includes circuitry for receiving and sending input and output signals to other components 155, such as hardware interrupts, system control signals, peripheral interfaces, co-processor control and/or data signals (e.g., signals for a graphics processing unit, floating point coprocessor, physics processing unit, digital signal processor, or other co-processing components), clock signals, semaphores, or other suitable I/O signals. The I/O signals may be synchronous or asynchronous. In some examples, all or a portion of the I/O interface is implemented using memory-mapped I/O techniques in conjunction with the memory interface 140. In some examples the I/O signal implementation is not limited to full swing electrical digital signals, but the I/O interface 150 can be configured to provide differential signals, pulsed signals, or other suitable signals for transmitting data and control signals.

The block-based processor 100 can also include a control unit 160. The control unit 160 supervises operation of the processor 100. Operations that can be performed by the control unit 160 can include allocation and de-allocation of cores for performing instruction processing, control of input data and output data between any of the cores, register files, the memory interface 140, and/or the I/O interface 150, modification of execution flow, and verifying target location(s) of branch instructions, instruction headers, and other changes in control flow. The control unit 160 can generate and control the processor according to control flow and metadata information representing exit points and control flow probabilities for instruction blocks. The control unit can be used to control data flow between general-purpose portions of the processor cores 110 and custom function blocks of the cores.

The control unit 160 can also process hardware interrupts, and control reading and writing of special system registers, for example a program counter stored in one or more register file(s). In some examples of the disclosed technology, the control unit 160 is at least partially implemented using one or more of the processing cores 110, while in other examples, the control unit 160 is implemented using a non-block-based processing core (e.g., a general-purpose RISC processing core coupled to memory, a hard macro processor block provided in an FPGA, or a general purpose soft processor). In some examples, the control unit 160 is implemented at least in part using one or more of: hardwired finite state machines, programmable microcode, programmable gate arrays, or other suitable control circuits. In alternative examples, control unit functionality can be performed by one or more of the cores 110.

The control unit 160 includes a number of schedulers 165-168 that are used to control instruction pipelines of the processor cores 110. In other examples, schedulers can be arranged so that they are contained with each individual processor core. As used herein, scheduler block allocation refers to directing operation of an instruction blocks, including initiating instruction block mapping, fetching, decoding, execution, committing, aborting, idling, and refreshing an instruction block. Further, instruction scheduling refers to scheduling the issuance and execution of instructions within an instruction block. For example, based on instruction dependencies and data indicating a relative ordering for memory access instructions, the control unit 160 can determine which instruction(s) in an instruction block are ready to issue and initiate issuance and execution of the instructions. Processor cores 110 are assigned to instruction blocks during instruction block mapping. The recited stages of instruction operation are for illustrative purposes and in some examples of the disclosed technology, certain operations can be combined, omitted, separated into multiple operations, or additional operations added. Each of the schedulers 165-168 schedules the flow of instructions, including allocation and de-allocation of cores for performing instruction processing, control of input data and output data between any of the cores, register files, the memory interface 140, and/or the I/O interface 150. Custom function blocks implemented by the cores 110 can send instruction identifiers, valid bits, and other information to one or more of the schedulers 165-168 to facilitation determinations of whether instruction dependencies for an instruction block have been satisfied, thereby allowing scheduling of dependent instructions.

The block-based processor 100 also includes a clock generator 170, which distributes one or more clock signals to various components within the processor (e.g., the cores 110, interconnect 120, memory interface 140, and I/O interface 150). In some examples of the disclosed technology, all of the components share a common clock, while in other examples different components use a different clock, for example, a clock signal having differing clock frequencies. In some examples, a portion of the clock is gated to allowing power savings when some of the processor components are not in use. In some examples, the clock signals are generated using a phase-locked loop (PLL) to generate a signal of fixed, constant frequency and duty cycle. Circuitry that receives the clock signals can be triggered on a single edge (e.g., a rising edge) while in other examples, at least some of the receiving circuitry is triggered by rising and falling clock edges. In some examples, the clock signal can be transmitted optically or wirelessly.

IV. Example Block-Based Processor Microarchitecture

FIG. 2 is a block diagram further detailing an example microarchitecture 200 for implementing the block-based processor 100, and in particular, an instance of one of the block-based processor cores, as can be used in certain examples of the disclosed technology. For ease of explanation, the exemplary microarchitecture has five pipeline stages including: instruction fetch (IF), decode (DC), issue, including operand fetch (IS), execute (EX), and memory/data access (LS). However, it will be readily understood by one of ordinary skill in the relevant art that modifications to the illustrated microarchitecture, such as adding/removing stages, adding/removing units that perform operations, and other implementation details can be modified to suit a particular application for a block-based processor.

As shown in FIG. 2, the processor core includes an instruction cache 210 that is coupled to an instruction decoder 220. The instruction cache 210 is configured to receive block-based processor instructions from a memory. In some FPGA implementations, the instruction cache can be implemented by a dual read port, dual write port, 18 or 36 Kb (kilobit), 32-bit wide block RAM. In some examples, the physical block RAM is configured to operate as two or more smaller block RAMs.

The processor core further includes an instruction window 230, which includes an instruction scheduler 235, a decoded instruction store 236, and a plurality of operand buffers 239. In FPGA implementations, each of these instruction window components 230 can be implemented including the use of LUT RAM (e.g., with SRAM configured as lookup tables) or BRAM (block RAM). The instruction scheduler 235 can send an instruction identifier (instruction ID or IID) for an instruction to the decoded instruction store 236 and the operand buffers 239 as a control signal. As discussed further below, each instruction in an instruction block has an associated instruction identifier that uniquely identifies the instruction within the instruction block. In some examples, instruction targets for sending the result of executing an instruction are encoded in the instruction. In this way, dependencies between instructions can be tracked using the instruction identifier instead of monitoring register dependencies. In some examples, the processor core can include two or more instruction windows. In some examples, the processor core can include one instruction window with multiple block contexts.

As will be discussed further below, the microarchitecture 200 includes a register file 290 that stores data for registers defined in the block-based processor architecture, and can have one or more read ports and one or more write ports. Because an instruction block executes on a transactional basis, changes to register values made by an instance of an instruction block are not visible to the same instance; the register writes will be committed upon completing execution of the instruction block.

The example microarchitecture 200 also includes a hardware profiler 295. The hardware profiler 295 can collect information about programs that execute on the processor. For examples, data regarding events, function calls, memory locations, and other information can be collected (e.g., using hardware instrumentation such as registers, counters, and other circuits) and analyzed to determine which portions of a program might be optimized. For example, a program can be optimized by mapping instructions or instruction blocks to one or more custom function units (e.g., custom function units 258 and 268) it improve execution speed and/or energy consumption.

The decoded instruction store 236 stores decoded signals for controlling operation of hardware components in the processor pipeline. For example, a 32-bit instruction may be decoded into 128-bits of decoded instruction data. The decoded instruction data is generated by the decoder 220 after an instruction is fetched. The operand buffers 239 store operands (e.g., register values received from the register file, data received from memory, immediate operands coded within an instruction, operands calculated by an earlier-issued instruction, or other operand values) until their respective decoded instructions are ready to execute. Instruction operands and predicates for the execute phase of the pipeline are read from the operand buffers 239, respectively, not (directly, at least) from the register file 290. The instruction window 230 can include a buffer for predicates directed to an instruction, including wired-OR logic for combining predicates sent to an instruction by multiple instructions.

In some examples, all of the instruction operands, except for register read operations, are read from the operand buffers 239 instead of the register file. In some examples the values are maintained until the instruction issues and the operand is communicated to the execution pipeline. In some FPGA examples, the decoded instruction store 236 and operand buffers 239 are implemented with a plurality of LUT RAMs.

The instruction scheduler 235 maintains a record of ready state of each decoded instruction's dependencies (e.g., the instruction's predicate and data operands). When all of the instruction's dependencies (if any) are satisfied, the instruction wakes up and is ready to issue. In some examples, the lowest numbered ready instruction ID is selected each pipeline clock cycle and its decoded instruction data and input operands are read. Besides the data mux and function unit control signals, the decoded instruction data can encode up to two ready events in the illustrated example. The instruction scheduler 235 accepts these and/or events from other sources (selected for input to the scheduler on inputs T0 and T1 with multiplexers 237 and 238, respectively) and updates the ready state of other instructions in the window. Thus dataflow execution proceeds, starting with the instruction block's ready zero-input instructions, then instructions that these instructions target, and so forth. Some instructions are ready to issue immediately (e.g., move immediate instructions) as they have no dependencies. Depending on the ISA, control structures, and other factors, the decoded instruction store 236 is about 100 bits wide in some examples, and includes information on instruction dependencies, including data indicating which target instruction(s)'s active ready state will be set as a result of issuing the instruction.

As used herein, ready state refers to processor state that indicates, for a given instruction, whether and which of its operands (if any) are ready, and whether the instruction itself is now ready for issue. In some examples, ready state includes decoded ready state and active ready state. Decoded ready state data is initialized by decoding instruction(s). Active ready state represents the set of input operands of an instruction that have been evaluated so far during the execution of the current instance of an instruction block. A respective instruction's active ready state is set by executing instruction(s) which target, for example, the left, right, and/or predicate operands of the respective instruction.

Attributes of the instruction window 230 and instruction scheduler 235, such as area, clock period, and capabilities can have significant impact to the realized performance of an EDGE core and the throughput of an EDGE multiprocessor. In some examples, the front end (IF, DC) portions of the microarchitecture can run decoupled from the back end portions of the microarchitecture (IS, EX, LS). In some FPGA implementations, the instruction window 230 is configured to fetch and decode two instructions per clock into the instruction window.

The instruction scheduler 235 has diverse functionality and requirements. It can be highly concurrent. Each clock cycle, the instruction decoder 220 writes decoded ready state and decoded instruction data for one or more instructions into the instruction window 230. Each clock cycle, the instruction scheduler 235 selects the next instruction(s) to issue, and in response the back end sends ready events, for example, target ready events targeting a specific instruction's input slot (e.g., predicate slot, right operand (OP0), or left operand (OP1)), or broadcast ready events targeting all instructions waiting on a broadcast ID. These events cause per-instruction active ready state bits to be set that, together with the decoded ready state, can be used to signal that the corresponding instruction is ready to issue. The instruction scheduler 235 sometimes accepts events for target instructions which have not yet been decoded, and the scheduler can also can also inhibit reissue of issued ready instructions.

Control circuits (e.g., signals generated using the decoded instruction store 236) in the instruction window 230 are used to generate control signals to regulate core operation (including, e.g., control of datapath and multiplexer select signals) and to schedule the flow of instructions within the core. This can include generating and using memory access instruction encodings, allocation and de-allocation of cores for performing instruction processing, control of input data and output data between any of the cores 110, register files, the memory interface 140, and/or the I/O interface 150.

In some examples, the instruction scheduler 235 is implemented as a finite state machine coupled to the other instruction window logic. In some examples, the instruction scheduler is mapped to one or more banks of RAM in an FPGA, and can be implemented with block RAM, LUT RAM, or other reconfigurable RAM. As will be readily apparent to one of ordinary skill in the relevant art, other circuit structures, implemented in an integrated circuit, programmable logic, or other suitable logic can be used to implement hardware for the instruction scheduler 235. In some examples of the disclosed technology, front-end pipeline stages IF and DC can run decoupled from the back-end pipelines stages (IS, EX, LS).

In the example of FIG. 2, the operand buffers 239 send the data operands, which can be designated left operand (LOP) and right operand (ROP) for convenience, to a set of execution state pipeline registers 245 via one or more switches (e.g., multiplexers 241 and 242). These operands can also be referred to as OP1 and OP0, respectively. A first router 240 is used to send data from the operand buffers 239 to one or more of the functional units 250, which can include but are not limited to, integer ALUs (arithmetic logic units) (e.g., integer ALUs 255), floating point units (e.g., floating point ALU 256), shift/rotate logic (e.g., barrel shifter 257), or other suitable execution units, which can including graphics functions, physics functions, and other mathematical operations. In some examples, a programmable execution unit 258 can be reconfigured to implement a number of different arbitrary functions (e.g., a priori or at runtime).

Data from the functional units 250 can then be routed through a second router (not shown) to a set of load/store pipeline registers 260, to a load/store queue 270 (e.g., for performing memory load and memory store operations), or fed back to the execution pipeline registers, thereby bypassing the operand buffers 239. The load/store queue 270 is coupled to a data cache 275 that caches data for memory operations. The outputs of the data cache 275, and the load/store pipelines registers 260 can be sent to a third router 280, which in turn sends data to the register file 290, the operand buffers 239, and/or the execution pipeline registers 245, according to the instruction being executed in the pipeline stage.

When execution of an instruction block is complete, the instruction block is designated as “committed” and signals from the control outputs can in turn can be used by other cores within the block-based processor 100 and/or by the control unit 160 to initiate scheduling, fetching, and execution of other instruction blocks.

As will be readily understood to one of ordinary skill in the relevant art, the components within an individual core are not limited to those shown in FIG. 2, but can be varied according to the requirements of a particular application. For example, a core may have fewer or more instruction windows, a single instruction decoder might be shared by two or more instruction windows, and the number of and type of functional units used can be varied, depending on the particular targeted application for the block-based processor. Other considerations that apply in selecting and allocating resources with an instruction core include performance requirements, energy usage requirements, integrated circuit die, process technology, and/or cost.

It will be readily apparent to one of ordinary skill in the relevant art that trade-offs can be made in processor performance by the design and allocation of resources within the instruction window and control unit of the processor cores 110. The area, clock period, capabilities, and limitations substantially determine the realized performance of the individual cores 110 and the throughput of the block-based processor 100.

Updates to the visible architectural state of the processor (such as to the register file 290 and the memory) affected by the executed instructions can be buffered locally within the core until the instructions are committed. The control circuitry can determine when instructions are ready to be committed, sequence the commit logic, and issue a commit signal. For example, a commit phase for an instruction block can begin when all register writes are buffered, all writes to memory (including unconditional and conditional stores) are buffered, and a branch target is calculated. The instruction block can be committed when updates to the visible architectural state are complete. For example, an instruction block can be committed when the register writes are written to as the register file, the stores are sent to a load/store unit or memory controller, and the commit signal is generated. The control circuit also controls, at least in part, allocation of functional units to the instructions window.

Because the instruction block is committed (or aborted) as an atomic transactional unit, it should be noted that results of certain operations are not available to instructions within an instruction block. This is in contrast to RISC and CISC architectures that provide results visible on an individual, instruction-by-instruction basis. Thus, additional techniques are disclosed for supporting memory synchronization and other memory operations in a block-based processor environment.

In some examples, block-based instructions can be non-predicated, or predicated true or false. A predicated instruction does not become ready until it is targeted by another instruction's predicate result, and that result matches the predicate condition. If the instruction's predicate does not match, then the instruction never issues.

In some examples, upon branching to a new instruction block, all instruction window ready state (stored in the instruction scheduler 235) is flash cleared (block reset). However when a block branches back to itself (block refresh), only active ready state is cleared; the decoded ready state is preserved so that it is not necessary to re-fetch and decode the blocks instructions. Thus, refresh can be used to save time and energy in loops, instead of performing a block reset.

Since some software critical paths include a single chain of dependent instructions (for example, instruction A targets instruction B, which in turn targets instruction C), it is often desirable that the dataflow scheduler not add pipeline bubbles for successive back-to-back instruction wakeup. In such cases, the IS-stage ready-issue-target-ready pipeline recurrence should complete in one cycle, assuming that this does not severely affect clock frequency.

Instructions such as ADD have a latency of one cycle. With EX-stage result forwarding, the scheduler can wake their targets' instructions in the IS-stage, even before the instruction completes. Other instruction results may await ALU comparisons, take multiple cycles, or have unknown latency. These instructions wait until later to wake their targets.

Finally, the scheduler design can be scalable across a spectrum of EDGE ISAs. In some examples, each pipeline cycle can accept from one to four decoded instructions and from two to four target ready events, and issue one to two instructions per cycle.

A number of different technologies can be used to implement the instruction scheduler 235. For example, the scheduler 235 can be implemented as a parallel scheduler, where instructions' ready state is explicitly represented in FPGA D-type flip-flops (FFs), and in which the ready status of every instruction is reevaluated each cycle. In other examples, the instruction scheduler 235 can be implemented as a more compact incremental scheduler that keeps ready state in LUT RAM and which updates ready status of about two to four target instructions per cycle.

The register file 290 may include two or more write ports for storing data in the register file, as well as having a plurality of read ports for reading data from individual registers within the register file. In some examples, a single instruction window (e.g., instruction window 230) can access only one port of the register file at a time, while in other examples, the instruction window 230 can access one read port and one write port, or can access two or more read ports and/or write ports simultaneously. In some examples, the microarchitecture is configured such that not all the read ports of the register 290 can use the bypass mechanism. For the example microarchitecture 200 shown in FIG. 2, the register file can send register data on the bypass path to one of the multiplexers 242 for the operand OP0, but not operand OP1. Thus, for multiple register reads in one cycle, only one operand can use the bypass, while the other register read results are sent to the operand buffers 239, which inserts an extra clock cycle in the instruction pipeline.

In some examples, the register file 290 can include 64 registers, each of the registers holding a word of 32 bits of data. (For convenient explanation, this application will refer to 32-bits of data as a word, unless otherwise specified. Suitable processors according to the disclosed technology could operate with 8-, 16-, 64-, 128-, 256-bit, or another number of bits words) In some examples, some of the registers within the register file 290 may be allocated to special purposes. For example, some of the registers can be dedicated as system registers examples of which include registers storing constant values (e.g., an all zero word), program counter(s) (PC), which indicate the current address of a program thread that is being executed, a physical core number, a logical core number, a core assignment topology, core control flags, execution flags, a processor topology, or other suitable dedicated purpose. In some examples, the register file 290 is implemented as an array of flip-flops, while in other examples, the register file can be implemented using latches, SRAM, FPGA LUT RAM, FPGA block RAM, or other forms of memory storage. The ISA specification for a given processor specifies how registers within the register file 290 are defined and used.

V. Example Field Programmable Gate Array Architecture

FIG. 3 is a block diagram 300 that depicts an example field programmable gate array (FPGA) architecture that is configured to implement certain examples of the disclosed technology. For example, the block-based processor 100 discussed above regarding FIG. 1, including those examples that used the microarchitecture 200 depicted in FIG. 2 can be mapped to the FPGA architecture of FIG. 3.

The FPGA includes an array of reconfigurable logic blocks arranged in an array. For example, the FPGA includes a first row of logic blocks, including logic blocks 310, 311, and 319, and a second row of logic blocks including logic blocks 320, 321, and 329. Each of the logic blocks includes logic that can be reconfigured to implement arbitrary logic functions and can also include sequential logic elements such as latches, flip-flops, and memories. The logic blocks are interconnected to each other using a routing fabric that includes a number of interconnect switches that can also be programmable. For example, there is a first row of switch blocks 330, 331, 332, etc., positioned between the first row of reconfigurable logic blocks and the second row of reconfigurable logic blocks. The switches can be configured in order to change wire connections that carry signals between the reconfigurable logic blocks. For example, instructions schedulers, functional units, pipeline buffers, and operand buffers can be mapped to the logic blocks connected using the switch blocks of FIG. 3.

The FPGA also includes a number of more complex components. For example, the logic block includes a number of block RAMs, for example, block RAM 340 and block RAM 349. The block RAMs typically contain a larger number of memory bits, for example, a few thousand memory bits that are accessed by applying an address to the memory, and reading from one or more read ports. In some examples, the block RAMs can include two or more write ports and two or more read ports. In other examples, the block RAMs may only have a single read and/or a single write port. While the block RAMs are typically accessed by applying an address and reading corresponding data, in some examples, the block RAMs can be configured with additional circuitry that allows for implementation of more complex functions including shift registers and First-In First-Out (FIFO) buffers.

The illustrated FPGA also includes a number of hard macro blocks including hard macro block 350 and hard macro block 359. These macro blocks can include more complex functionality such as processor functionality, digital signal processing functionality, accelerators, or other functions deemed to be desirable. The illustrated FPGA further includes a configuration port 360 that can be used to reprogram logic devices in the FPGA. In some examples, configuration memories that store configuration information for the logic devices can be addressed and read/written to directly. In other examples, a scan chain architecture is used to store configuration information in a serial manner.

The FPGA is further surrounded by an I/O ring 370 that can be coupled to the logic blocks, the block rams, and/or the hard macro blocks in order to receive and send signals to components away from the FPGA. In some examples, the I/O signals are full rail voltage signals, while other examples, differential signals are used. In some examples, the I/O ports can be multiplexed (e.g. time-multiplexed) in order to support input and output of more signals than the number of pins available on the FPGA.

While many examples of FPGAs are typically reconfigurable an arbitrary number of times through the use of electrically erasable memories, in other examples, one-time programmable logic elements can be used. For example, the logic blocks and switches can be programmed with the use of fuses, anti-fuses, or with a ROM mask to program a logic function once that is not easily reversible.

In the reconfigurable case, the FPGA typically has a configuration port that receives data according to a file dubbed a bitstream, or a configuration bitstream. The bitstream data is read into the device and used to program and configure the logic blocks, the switches, the block rams, and/or the hard macros. When a new design is desired, the configuration can be erased and a new design configured into the device. In some examples, the FPGA can be partially reconfigured in order to save on programming time. For example, a subset of the logic blocks, the switches, or block rams can be dynamically reconfigured in the field without reprogramming the entire device.

One challenge for block-based processor implementations mapped onto reconfigurable logic is determining micro-architectural structures that can be efficiently implemented using the available blocks of a custom or off-the-shelf device. However, using the disclosed technologies, higher performance, and/or more efficient structures can be implemented. Further, it should be readily understood that while some examples of the FPGAs are a stand-alone integrated circuit, in other examples, the FPGA may be packaged differently, for example, in a multi-chip module (MCM), or on the same circuit die as a custom or basic system-on-chip (SoC).

FIG. 4 is a block diagram 400 illustrating four reconfigurable logic blocks 410, 411, 412, and 413 that can configured to form part of the logic fabric of an example FPGA-integrated circuit. The components inside the reconfigurable logic blocks shown are identical, or homogenous, but it should be readily understood, in other examples, more than one type of reconfigurable logic block may be present on a single FPGA.

A first reconfigurable logic block 410 includes a six-input Look Up Table (LUT) 420 that is coupled to carry logic 430, a number of multiplexers 440 and 445, and a storage element (here, a D flip-flop) 450. The LUT 420 can be implemented using a small memory (for example, a memory having six address bits and two output bits as shown). Thus, any six-input Boolean function can be implemented by using a single LUT. In some examples, outputs of LUTs can be combined, or a reconfigurable logic block can have multiple LUTs that can be connected together in order to perform more complex logic functions. In some examples, common logic functions can be providing in addition to the LUT. For example, the carry logic 430 can be configured to perform the carry propagation logic for an adder. The multiplexers are used to select various output from other components. For example, the multiplexer 440 can be used to select the output of either the LUT 420 or the carry logic 430, while the multiplexer 445 can be used to select another output of the LUT 420 or the multiplexer 440. In some examples, the multiplexer is used to either select a sequential output of a state element (e.g. flip-flop 450), or a combinational output of a Look Up Table. It should be readily understood to one of ordinary skill in the art that different logic functions, LUT sizes, and sequential elements can be employed in a reconfigurable logic element. Thus, techniques for mapping block-based processors to such reconfigurable logic can vary depending on the specific target FPGA architecture. The configuration of the logic inside the reconfigurable logic block can be programmed using the configuration port of the FPGA. In some examples, the LUTs are not programmed once, but can be configured to act as small memories that store certain data used in the block-based processor.

In some examples of the disclosed technology, a logic synthesis tool (logic compiler) is used to transform a specification for a block-processor into a configuration bitstream that can be applied to a configuration port of an FPGA to configure logic to implement a block-based processor. In some examples, the designer can use an RPM (relationally placed macro) methodology to improve area and interconnect delays and achieve a repeatable layout for easy routing and timing closure under module composition and massive replication. For example, by including structural RTL instantiating modules and tiling them into a scheduler, logic for the instruction scheduler can be locked to a set of single LUTs, allow for a compact clustering and placement of logic within the FPGA.

VI. Example Stream of Instruction Blocks

Turning now to the diagram 500 of FIG. 5, a portion 510 of a stream of block-based instructions, including a number of variable length instruction blocks 511-514 is illustrated. The stream of instructions can be used to implement user application, system services, or any other suitable use. The stream of instructions can be stored in memory, received from another process in memory, received over a network connection, or stored or received in any other suitable manner In the example shown in FIG. 5, each instruction block begins with an instruction header, which is followed by a varying number of instructions. For example, the instruction block 511 includes a header 520 and twenty instructions 521. The particular instruction header 520 illustrated includes a number of data fields that control, in part, execution of the instructions within the instruction block, and also allow for improved performance enhancement techniques including, for example branch prediction, speculative execution, lazy evaluation, and/or other techniques. The instruction header 520 also includes an indication of the instruction block size. The instruction block size can be in larger chunks of instructions than one, for example, the number of 4-instruction chunks contained within the instruction block. In other words, the size of the block is shifted 4 bits in order to compress header space allocated to specifying instruction block size. Thus, a size value of 0 indicates a minimally-sized instruction block which is a block header followed by four instructions. In some examples, the instruction block size is expressed as a number of bytes, as a number of words, as a number of n-word chunks, as an address, as an address offset, or using other suitable expressions for describing the size of instruction blocks. In some examples, the instruction block size is indicated by a terminating bit pattern in the instruction block header and/or footer.

The instruction block header 520 can also include one or more execution flags that indicate one or more modes of operation for executing the instruction block. For example, the modes of operation can include core fusion operation, vector mode operation, memory dependence prediction, and/or in-order or deterministic instruction execution. Further, the execution flags can include a block synchronization flag that inhibits speculative execution of the instruction block.

In some examples of the disclosed technology, the instruction header 520 includes one or more identification bits that indicate that the encoded data is an instruction header. For example, in some block-based processor ISAs, a single ID bit in the least significant bit space is always set to the binary value 1 to indicate the beginning of a valid instruction block. In other examples, different bit encodings can be used for the identification bit(s). In some examples, the instruction header 520 includes information indicating a particular version of the ISA for which the associated instruction block is encoded.

In some examples of the disclosed technology, a field of the block header 520 encodes data indicating that the block contains instructions to execute particular custom instructions that require a custom functional block or a particular custom function block to be present, preconfigured, or dynamically configured.

The block instruction header can also include a number of block exit types for use in, for example, branch prediction, control flow determination, and/or branch processing. The exit type can indicate what the type of branch instructions are, for example: sequential branch instructions, which point to the next contiguous instruction block in memory; offset instructions, which are branches to another instruction block at a memory address calculated relative to an offset; subroutine calls, or subroutine returns. By encoding the branch exit types in the instruction header, the branch predictor can begin operation, at least partially, before branch instructions within the same instruction block have been fetched and/or decoded.

The illustrated instruction block header 520 also includes a store mask that indicates which of the load-store queue identifiers encoded in the block instructions are assigned to store operations. The instruction block header can also include a write mask, which identifies which global register(s) the associated instruction block will write. In some examples, the store mask is stored in a store vector register by, for example, an instruction decoder (e.g., decoder 220). In other examples, the instruction block header 520 does not include the store mask, but the store mask is generated dynamically by the instruction decoder by analyzing instruction dependencies when the instruction block is decoded. For example, the decoder can generate load store identifiers for instruction block instructions to determine a store mask and store the store mask data in a store vector register. Similarly, in other examples, the write mask is not encoded in the instruction block header, but is generated dynamically (e.g., by analyzing registers referenced by instructions in the instruction block) by an instruction decoder) and stored in a write mask register. The write mask can be used to determine when execution of an instruction block has completed and thus to initiate commitment of the instruction block. The associated register file must receive a write to each entry before the instruction block can complete. In some examples a block-based processor architecture can include not only scalar instructions, but also single-instruction multiple-data (SIMD) instructions, that allow for operations with a larger number of data operands within a single instruction.

Examples of suitable block-based instructions that can be used for the instructions 521 can include instructions for executing integer and floating-point arithmetic, logical operations, type conversions, register reads and writes, memory loads and stores, execution of branches and jumps, and other suitable processor instructions. In some examples, the instructions include instructions for configuring the processor to operate according to one or more of operations by, for example, speculative. Because an instruction's dependencies are encoded in the instruction block (e.g., in the instruction block header, other instructions that target the instruction, and/or in the instruction itself), instructions can issue and execute out of program order when the instruction's dependencies are satisfied.

VII. Example Block Instruction Target Encoding

FIG. 6 is a diagram 600 depicting an example of two portions 610 and 615 of C language source code and their respective instruction blocks 620 and 625, illustrating how block-based instructions can explicitly encode their targets. In this example, the first two READ instructions 630 and 631 target the right (T[2R]) and left (T[2L]) operands, respectively, of the ADD instruction 632 (2R indicates targeting the right operand of instruction number 2; 2L indicates the left operand of instruction number 2). In the illustrated ISA, the read instruction is the only instruction that reads from the global register file (e.g., register file 290); however any instruction can target the global register file. When the ADD instruction 632 receives the results of both register reads it will become ready and execute. It is noted that the present disclosure sometimes refers to the right operand as OP0 and the left operand as OP1.

When the TLEI (test-less-than-equal-immediate) instruction 633 receives its single input operand from the ADD, it will become ready to issue and execute. The test then produces a predicate operand that is broadcast on channel one (B[1P]) to all instructions listening on the broadcast channel for the predicate, which in this example are the two predicated branch instructions (BRO_T 634 and BRO_F 635). The branch instruction that receives a matching predicate will issue, but the other instruction, encoded with the complementary predicated, will not issue.

A dependence graph 640 for the instruction block 620 is also illustrated, as an array 650 of instruction nodes and their corresponding operand targets 655 and 656. This illustrates the correspondence between the block instructions 620, the corresponding instruction window entries, and the underlying dataflow graph represented by the instructions. Here decoded instructions READ 630 and READ 631 are ready to issue, as they have no input dependencies. As they issue and execute, the values read from registers R0 and R7 are written into the right and left operand buffers of ADD 632, marking the left and right operands of ADD 632 “ready.” As a result, the ADD 632 instruction becomes ready, issues to an ALU, executes, and the sum is written to the left operand of the TLEI instruction 633.

VIII. Example Block-Based Instruction Formats

FIG. 7 is a diagram illustrating generalized examples of instruction formats for an instruction header 710, a generic instruction 720, a branch instruction 730, and a memory access instruction 740 (e.g., a memory load or store instruction). The instruction formats can be used for instruction blocks executed according to a number of execution flags specified in an instruction header that specify a mode of operation. Each of the instruction headers or instructions is labeled according to the number of bits. For example the instruction header 710 includes four 32-bit words and is labeled from its least significant bit (lsb) (bit 0) up to its most significant bit (msb) (bit 127). As shown, the instruction header includes a write mask field, a number of execution flag fields, an instruction block size field, and an instruction header ID bit (the least significant bit of the instruction header). In some examples, the instruction header 710 includes additional metadata 715 and/or 716, which can be used to control additional aspects of instruction block execution and performance. In some examples, the additional metadata is used to indicate that one or more instructions are fused. In some examples, the additional meta data is used to configure a custom function block. In some examples, the additional meta data is generated and/or used by a hardware or software profiler tool.

The execution flag fields depicted in FIG. 7 occupy bits 6 through 13 of the instruction block header 710 and indicate one or more modes of operation for executing the instruction block. For example, the modes of operation can include core fusion operation, vector mode operation, branch predictor inhibition, memory dependence predictor inhibition, block synchronization, break after block, break before block, block fall through, and/or in-order or deterministic instruction execution. The block synchronization flag occupies bit 9 of the instruction block and inhibits speculative execution of the instruction block when set to logic 1.

The exit type fields include data that can be used to indicate the types of control flow instructions encoded within the instruction block. For example, the exit type fields can indicate that the instruction block includes one or more of the following: sequential branch instructions, offset branch instructions, indirect branch instructions, call instructions, and/or return instructions. In some examples, the branch instructions can be any control flow instructions for transferring control flow between instruction blocks, including relative and/or absolute addresses, and using a conditional or unconditional predicate. The exit type fields can be used for branch prediction and speculative execution in addition to determining implicit control flow instructions.

The illustrated generic block instruction 720 is stored as one 32-bit word and includes an opcode field, a predicate field, a broadcast ID field (BID), a vector operation field (V), a single instruction multiple data (SIMD) field, a first target field (T1), and a second target field (T2). For instructions with more consumers than target fields, a compiler can build a fanout tree using move instructions, or it can assign high-fanout results to broadcasts. Broadcasts support sending an operand over a lightweight network to any number of consumer instructions in a core.

While the generic instruction format outlined by the generic instruction 720 can represent some or all instructions processed by a block-based processor, it will be readily understood by one of skill in the art that, even for a particular example of an ISA, one or more of the instruction fields may deviate from the generic format for particular instructions. The opcode field specifies the operation(s) performed by the instruction 720, such as memory read/write, register load/store, add, subtract, multiply, divide, shift, rotate, system operations, or other suitable instructions. The predicate field specifies the condition under which the instruction will execute. For example, the predicate field can specify the value “true,” and the instruction will only execute if a corresponding condition flag matches the specified predicate value. In some examples, the predicate field specifies, at least in part, which is used to compare the predicate, while in other examples, the execution is predicated on a flag set by a previous instruction (e.g., the preceding instruction in the instruction block). In some examples, the predicate field can specify that the instruction will always, or never, be executed. Thus, use of the predicate field can allow for denser object code, improved energy efficiency, and improved processor performance, by reducing the number of branch instructions.

The target fields T1 and T2 specify the instructions to which the results of the block-based instruction are sent. For example, an ADD instruction at instruction slot 7 can specify that its computed result will be sent to instructions at slots 3 and 10, including specification of the operand slot (e.g., left operation, right operand, or predicate operand). Depending on the particular instruction and ISA, one or both of the illustrated target fields can be replaced by other information, for example, the first target field T1 can be replaced by an immediate operand, an additional opcode, specify two targets, etc.

The branch instruction 730 includes an opcode field, a predicate field, a broadcast ID field (BID), and an offset field. The opcode and predicate fields are similar in format and function as described regarding the generic instruction. The offset can be expressed in units of groups of four instructions, thus extending the memory address range over which a branch can be executed. The predicate shown with the generic instruction 720 and the branch instruction 730 can be used to avoid additional branching within an instruction block. For example, execution of a particular instruction can be predicated on the result of a previous instruction (e.g., a comparison of two operands). If the predicate is false, the instruction will not commit values calculated by the particular instruction. If the predicate value does not match the required predicate, the instruction does not issue. For example, a BRO_F (predicated false) instruction will issue if it is sent a false predicate value.

It should be readily understood that, as used herein, the term “branch instruction” is not limited to changing program execution to a relative memory location, but also includes jumps to an absolute or symbolic memory location, subroutine calls and returns, and other instructions that can modify the execution flow. In some examples, the execution flow is modified by changing the value of a system register (e.g., a program counter PC or instruction pointer), while in other examples, the execution flow can be changed by modifying a value stored at a designated location in memory. In some examples, a jump register branch instruction is used to jump to a memory location stored in a register. In some examples, subroutine calls and returns are implemented using jump and link and jump register instructions, respectively.

The memory access instruction 740 format includes an opcode field, a predicate field, a broadcast ID field (BID), an immediate field (IMM), and a target field (T1). The opcode, broadcast, predicate fields are similar in format and function as described regarding the generic instruction. For example, execution of a particular instruction can be predicated on the result of a previous instruction (e.g., a comparison of two operands). If the predicate is false, the instruction will not commit values calculated by the particular instruction. If the predicate value does not match the required predicate, the instruction does not issue. The immediate field can be used as an offset for the operand sent to the load or store instruction. The operand plus (shifted) immediate offset is used as a memory address for the load/store instruction (e.g., an address to read data from, or store data to, in memory). For some instructions, an additional bit (e.g., encoded in an opcode or in another field of the instruction) is used to indicate whether an instruction is fused with one or more other instructions in an instruction block. Such fused instructions can be executed with a custom function block, as further detailed below. In some examples, certain fields from the instruction headers or instructions can be used to provide parameters configuring operation of a custom function block.

In some examples of the disclosed technology, object code for custom function blocks can be generated as follows. As will be readily understood to one of ordinary skill in the art, other suitable techniques can be used to generate such object code. A high level language compiler compiles a program into a series of instruction blocks (e.g., the instruction block discussed above regarding FIG. 5). The compiler is custom function aware and can pattern match expression tree templates to translate them into custom function unit instructions such as COMPLEX_MULTIPLY. In some examples, a programmer can explicitly call an intrinsic function that stands for the custom function (e.g., “Complex_cmul (const Complex& a, const Complex& b)”), so that the compiler translates every invocation of this _cmul instrinsic into a custom function unit instruction such as COMPLEX_MULTIPLY. In some examples, a compiler (guided by profile feedback) identifies hot spot code regions, defines a new custom function index for this function, synthesizes a custom logic datapath and finite state machine to control it, emits a custom function invoke instruction with the corresponding custom function index parameter, synthesizes the partial configuration bitstream for the custom function block comprising the custom function unit, copies the configuration bitstream into the program binary, and generates code or data to ensure the referenced custom function block's configuration bitstream is loaded whenever the custom function block is used. In some examples, a compiler generates a pure software version of the hot spot code region and also a version that issues the custom function invoke instruction with the corresponding custom function index parameter.

In some embodiments, a processor core (e.g., a processor core having the microarchitecture discussed below) 900 with a custom function block 910 will also include a full complement of standard function units (e.g. 255, 256, 256, 258, etc.) so that the processor core can still run all programs, as well as custom functions (e.g., custom function units 930-933).

In some examples, two versions of certain functions in the source code are produced by the compiler, one version which targets a base (non-customized) processor such that all source code that is compiled into the base instruction set architecture instructions executes on the base processor's pre-existing fixed function units, and a second version which includes custom function instructions which are executed using a customized processor with the corresponding custom function block. In some embodiments, the compiler also generates code to interrogate the current processor configuration and dynamically run a function using the first version of the machine code, or using the second (custom function unit) version, if the processor is so configured.

In some examples, libraries of such program code which execute on base processors, and, which execute faster on suitably customized processors, are provided so that software developers can simply call library functions without specific knowledge of the presence or type of custom function units present on any given processor.

IX. Example Processor State Diagram

FIG. 8 is a state diagram 800 illustrating number of states assigned to an instruction block as it is mapped, executed, and retired. For example, one or more of the states can be assigned during execution of an instruction according to one or more execution flags. It should be readily understood that the states shown in FIG. 8 are for one example of the disclosed technology, but that in other examples an instruction block may have additional or fewer states, as well as having different states than those depicted in the state diagram 800. At state 805, an instruction block is unmapped. The instruction block may be resident in memory coupled to a block-based processor, stored on a computer-readable storage device such as a hard drive or a flash drive, and can be local to the processor or located at a remote server and accessible using a computer network. The unmapped instructions may also be at least partially resident in a cache memory coupled to the block-based processor.

At instruction block map state 810, control logic for the block-based processor, such as an instruction scheduler, can be used to monitor processing core resources of the block-based processor and map the instruction block to one or more of the processing cores.

The control unit can map one or more of the instruction block to processor cores and/or instruction windows of particular processor cores. In some examples, the control unit monitors processor cores that have previously executed a particular instruction block and can re-use decoded instructions for the instruction block still resident on the “warmed up” processor core. Once the one or more instruction blocks have been mapped to processor cores, the instruction block can proceed to the fetch state 820.

When the instruction block is in the fetch state 820 (e.g., instruction fetch), the mapped processor core fetches computer-readable block instructions from the block-based processors' memory system and loads them into a memory associated with a particular processor core. For example, fetched instructions for the instruction block can be fetched and stored in an instruction cache within the processor core. The instructions can be communicated to the processor core using core interconnect. Once at least one instruction of the instruction block has been fetched, the instruction block can enter the instruction decode state 830.

During the instruction decode state 830, various bits of the fetched instruction are decoded into signals that can be used by the processor core to control execution of the particular instruction, including generation of identifiers indicating relative ordering of memory access instructions. For example, the decoded instructions can be stored in one of the memory stores shown above, in FIG. 2. The decoding includes generating dependencies for the decoded instruction, operand information for the decoded instruction, and targets for the decoded instruction. Once at least one instruction of the instruction block has been decoded, the instruction block can proceed to issue state 840.

During the issue state 840, instruction dependencies are evaluated to determine if an instruction is ready for execution. For example, an instruction scheduler can monitor an instruction's source operands and predicate operand (for predicated instructions) must be available before an instruction is ready to issue. For some encodings, certain instructions also must issue according to a specified ordering. For example, memory load store operations are ordered according to an LSID value encoded in each instruction. In some examples, more than one instruction is ready to issue simultaneously, and the instruction scheduler selects one of the ready to issue instructions to issue. Instructions can be identified using their IID to facilitate evaluation of instruction dependencies. Once at least one instruction of the instruction block has issued, source operands for the issued instruction(s) can be fetched (or sustained on a bypass path), and the instruction block can proceed to execution state 850.

During the execution state 850, operations associated with the instruction are performed using, for example, functional units 260 as discussed above regarding FIG. 2. As discussed above, the functions performed can include arithmetical functions, logical functions, branch instructions, memory operations, and register operations. Control logic associated with the processor core monitors execution of the instruction block, and once it is determined that the instruction block can either be committed, or the instruction block is to be aborted, the instruction block state is set to commit/abort state 860. In some examples, the control logic uses a write mask and/or a store mask for an instruction block to determine whether execution has proceeded sufficiently to commit the instruction block.

At the commit/abort state 860, the processor core control unit determines that operations performed by the instruction block can be completed. For example memory load store operations, register read/writes, branch instructions, and other instructions will definitely be performed according to the control flow of the instruction block. For conditional memory instructions, data will be written to memory, and a status indicator value that indicates success generated during the commit/abort state 860. Alternatively, if the instruction block is to be aborted, for example, because one or more of the dependencies of instructions are not satisfied, or the instruction was speculatively executed on a predicate for the instruction block that was not satisfied, the instruction block is aborted so that it will not affect the state of the sequence of instructions in memory or the register file. Regardless of whether the instruction block has committed or aborted, the instruction block goes to state 870 to determine whether the instruction block should be refreshed. If the instruction block is refreshed, the processor core re-executes the instruction block, typically using new data values, particularly the registers and memory updated by the just-committed execution of the block, and proceeds directly to the execution state 850. Thus, the time and energy spent in mapping, fetching, and decoding the instruction block can be avoided. Alternatively, if the instruction block is not to be refreshed, then the instruction block enters an idle state 880.

In the idle state 880, the processor core executing the instruction block can be idled by, for example, powering down hardware within the processor core, while maintaining at least a portion of the decoded instructions for the instruction block. At some point, the control unit determines 890 whether the idle instruction block on the processor core is to be refreshed or not. If the idle instruction block is to be refreshed, the instruction block can resume execution of instructions at issue state 840. Alternatively, if the instruction block is not to be refreshed, then the instruction block is unmapped and the processor core can be flushed and subsequently instruction blocks can be mapped to the flushed processor core.

While the state diagram 800 illustrates the states of an instruction block as executing on a single processor core for ease of explanation, it should be readily understood to one of ordinary skill in the relevant art that in certain examples, multiple processor cores can be used to execute multiple instances of a given instruction block, concurrently.

X. Example Microarchitecture with Custom Function Blocks

FIG. 9 is a block diagram detailing an example microarchitecture 900 that has been configured to include a custom function block 910, as can be used in certain examples of the disclosed technology. For example, the example microarchitecture 200 discussed above regarding FIG. 2 including programmable execution units 258 and 268 can be adapted to form the microarchitecture 900 depicted. In some examples, the custom function block 910 is implemented as a portion of a custom integrated circuit or as an ASIC. In some examples, the custom function block 910 is implemented using configurable logic including one-time programmable or many-time reprogrammable logic, such as in an FPGA.

As used herein, unless stated otherwise, the term “custom function block” is generally used to refer to a customizable portion of a block-based processer and associated data and control units. The term “custom function unit” refers to sub-components of a custom function block that are configured to provide a specific function, for example, a parameterized ALU, a specific ALU, an adder, multiplier, comparator, a look-up table, or other arbitrary arithmetic, logic, or other data processing function, and/or a custom RAM, FIFO queue, or other interconnect.

As shown in the example of FIG. 9, data operands (e.g., OP0-0, OP0-1, OP1-0, and OP1-1) are temporarily stored in the operand buffers 239. In the example shown, a multiplication operation on two complex numbers is being performed: (x+yi)×(u+vi). Data from the operand buffers 239 can be sent to the custom function block 910 via multiplexers 241 and 242. The data is sent to a series of pipeline registers 245, such as those discussed above regarding FIG. 2. In some examples, the custom function block shares a set of pipeline registers with the general-purpose execution units of the block-based processor. In other examples, the custom function block includes its own set of pipeline registers that store data received from the operand buffers. Data from the operand buffers 239 can also be sent to a set of parameter registers 920. The parameter registers 920 can be used to specify functions performed by the custom function block. For example, suitable parameters include vectorization, single data or multiple data instructions, whether an instruction is fused, specific functions such as arithmetic and logical operations, width of input and/or output data fields, rounding modes, constant coefficients, lookup table contents, memory configuration, or other suitable parameters.

The illustrated shared pipeline registers can in turn send data to generic functional units, including the integer ALU 255 as well as custom function units 930 through 933 as shown. In the illustrated example, the custom function block 910 has been configured to perform multiplication of two complex numbers. The custom function units 930 through 933 produce intermediate product values: xv, yu, xu, and yv. These intermediate values are sent to a set of load-store-stage pipeline registers 260. A second stage of operations is then performed using custom function units 940 and 941, which are configured to perform an add (xv+yu) and a subtract (xu−yv) operation, respectively. By reprogramming the underlying logic circuits, the custom function block 910 can be programmed to perform implement a large number of different arbitrary functions. For example, the logic underlying the function units can be reprogrammed during operation of the processor, prior to initiating an instruction block, prior to initiating use of the processor, or at another suitable interval for reprogramming the logic, depending on the performance requirements and configurability of the underlying configurable logic. The computed values are in turn sent to a router 280 and can then be stored back in the operand buffers 239, in the load store queue 270, and/or in the register file 290.

The custom function block 910 also includes a control signal generator which generates one or more instruction completion signals that can be sent to the instruction scheduler 235 and/or the custom control unit 905. The instruction completion signal can be used to identify (1) the issued (and now completed) custom function instruction and/or (2) the targets of the instruction. In block-based and EDGE architectures such as those disclosed herein, the targets may be data values or predicates, and can be identified as (other) instructions' operands, broadcast channels, or registers to write. Upon executing a block that specifies a custom function block, that is not yet so configured, the custom control circuit 905 can copy the custom function block's partial reconfiguration bitstream into the device's configuration port to load it into the reconfigurable logic.

The consistent use of custom function block completion signals enables uniform and efficient dataflow scheduling of instructions across arbitrary custom function units with single-cycle, multiple-cycle, or varying or unpredictable operation latencies (including out-of-order completion) alongside the processor's other fixed function units. When an instruction issues, whether fixed or custom function, its completion leads to the write-back of its results to the appropriate targets and the making-ready, waking, and issuance of instructions that consume its results. In some examples, the completion signal is a simple done signal that indicates completion of the custom function operation.

In some examples, the completion signal includes the IID of the issued instruction, validated by a validity signal V. More complex completion signals such as these can be useful if many or varied latency custom functions are in flight concurrently. The processor core, and in particular the processor core instruction scheduler, can map this IID into the custom instruction's targets information. This can include the type of data (e.g., value or predicate) and target location (e.g., a specific operand of another pending instruction, or a specific-operand broadcast channel). This can be used by the instruction scheduler to update and perhaps wake and issue any target(s) of the custom function instruction. In some examples, the completion signal is the instruction's target information itself. This can be used directly by the instruction scheduler to update and perhaps wake and issue any target(s) of the custom function instruction.

Examples of ready state data include target instruction ID identifiers (IID) and valid bits, which indicate that the operation specified for the custom function block has been completed. By generating the ready state data with the control signal generator 950, an arbitrary number of custom function blocks can be added to a block-based processor using a consistent interface to allow seamless addition of custom functions with generic functions specified by general purpose instructions of the block-based processor.

The block-based microarchitecture 900 also includes a profiler 295, which can be implemented with hardware and/or software resources. The profiler monitors execution of programs with the block-based processor to identify hot spots or other areas of an instruction stream that is highly suitable for optimization. Based on information captured with the profiler 295, portions of one or more instruction blocks defined using general purpose instructions can be mapped to the custom function block 910, thereby improving execution speed and/or energy consumption.

XI. Example with Custom Function Block and Fused Instructions

FIG. 10 includes a block diagram 1000 of a custom function block 1010 that has been configured to perform operations using two fused instructions. The custom function block 1010 includes a custom control circuit 1015 that generates control signals for operating components of the data path of the unit and parameter registers 1017 that store parameter values that specify certain aspects of operating the custom function block 1010.

In processors that can be extended with custom function blocks, it is sometimes advantageous for the processor design to accommodate not only 0-, 1-, and 2-input operand instructions, but also to accommodate instructions with more inputs, such as 3-input multiply-add (a*b+c) or 8-input 4-vector-dot-product (a0*b0+a1*b1+a2*b2+a3*b3). Accordingly, such examples can use a series of “fused” instructions to collect the (greater than two) number input operands across several instructions and their operand buffers, that then issue together, either simultaneously or in a tightly pipelined fashion.

As shown in FIG. 10, a portion of source code (reproduced below in Table I) 1020 includes a number of block-based processor instructions including two fused instructions labeled I[3] and I[4].

TABLE I I [0] READ R0 T [3R] I [1] READ R1 T [3L] I [2] READ R2 T [4L] I [3] FU_MUL T [4R] I [4] FU_ADD #P T [5R]

The fused instructions are for a complex multiply-add operation A×B+C. There are four operands used by the two fused instructions including OP0-1, storing B, OP0-0, storing A, OP1-0, storing C, and OP1-1, storing a parameter P. The operands are received by the custom function block 1010. The operands A, B, and C are sent to custom execution units 1030 and 1035. The custom control circuits 1015 controls sequencing of fused operations. The parameter P is sent to the parameter registers 1017. Parameter P can be used to specify or configure an aspect of the fused operation, including the specific operation to perform from amongst a set of possible operations. In the illustrated case, the parameter P can be used to specify that the instructions are for a single instruction multiple data (SIMD) operation (e.g., a SIMD operation where operands A, B, and C each represent 4 8-bit integers instead of a single 32-bit integer). In other examples, the parameter can set other aspects of the fused operation such as whether the instructions are signed, vectorized, integer or fixed-point, or other suitable parameter. The custom control circuit 1015 controls sequencing to optimize execution using the custom function block 1010. For example, the custom control circuit 1015 can ensure that the first fused multiply instruction I[3] is executed immediately before the subsequent fused add instruction I[4]. Thus, The product A×B can bypass the operand buffers 239 and be sent directly to the pipeline registers 245 for loading by the execution unit 1035, which is configured to add the product A×B to the value C. It should be noted that the output A×B+C is typically not generated until one or more clock cycles after the product A×B is generated by the execution unit 1030.

In some examples, the custom control circuit 1015 delays issue of a first instruction of a set of two or more fused instructions even though the first instruction has all of its dependencies satisfied. The custom control circuit 1015 determines that a second instruction of the set of fused instructions has its dependencies satisfied at a later point, and subsequently, the custom control unit issues the delayed first instruction. The first instruction, once executed, generates an operand that is consumed by the second instruction. Thus, by delaying issue of a first instruction of a set of fused instructions, additional delay caused by writing and reading to the operand buffers can be avoided using a bypass mechanism. In some examples, the custom control circuit 1015 causes issue of a first instruction of a set of two or more fused instructions that specifies the use of a custom function block. A second instruction of the set of fused instruction is then issued, the second instruction being issued in a sequence that allows bypass of the operand buffer.

In some examples, the number of read ports on the left and right operand buffers is increased so that upon issuance of an instruction that consumes (for example) four input operands, all four operands may be read from the operand buffers in a single cycle, enabling issue and execution of 4-input custom functions at an initiation interval (cadence) of one instruction per cycle (per custom function unit). In some examples, the number of operand buffers per instruction is increased from two to a higher number, so that instead of forming fused instructions from multiple 2-input functions as described above, a custom function of four inputs may be directly represented in a single instruction, and so that as many as every instruction in a block may be a 4-input custom function. Thus, the uniform application of the dataflow instruction scheduler and explicit target information and target ready events enables a regular microarchitecture, scheduling, and result write back across both 2-input fixed function units and multi-input multi-cycle-latency custom function units.

XII. Example Block-Based Processor System and Custom Function Blocks

FIG. 11 is a diagram 1100 illustrating an apparatus comprising a block-based processor 1110, including a control unit 1120 configured to execute instruction blocks including instructions for memory operations including memory synchronization and memory locks. The control unit includes a core scheduler 1125 that controls allocation and de-allocation of cores for performing instruction processing, control of input data and output data between any of the cores, register files, memory interfaces and/or I/O interfaces. The control unit 1120 can also include dedicated registers for performing certain memory operations.

The block-based processor 1110 also includes one or more processer cores 1130-1137 that are configured to fetch and execute instruction blocks. Each of the cores includes an instruction scheduler (e.g., parallel instruction scheduler 1141) that controls the order in which instructions in an instruction block are fetched, decoded, issued, and executed. The illustrated block-based processor 1110 has up to eight cores, but in other examples there could be 1, 2, 4, 64, 512, 1024, or other numbers of block-based processor cores. Each of the cores 1130-37 can be configured and/or reconfigured to perform programmed functions defined for one or more custom function blocks (e.g., custom function block 1145). The custom function blocks can be implemented using reconfigurable logic, such as reprogrammable memories in FPGA-like structures.

The block-based processor 1110 is coupled to a memory 1150 which includes a number of instruction blocks, including instruction blocks A and B, which include instructions (1155 and 1156, respectively) implementing disclosed memory operations, and to a computer-readable storage media disc 1160 that stores instructions 1165 for performing disclosed memory operations. Further, the memory 1150 and media disc 1160 can store configuration information for programming custom function blocks of the cores. For example, a hardware description language can be compiled into a configuration bitstream that is applied to a configuration port of one or more of the processor cores 1130-37. In some examples, a dynamically-generated partial reconfiguration bitstream for one or more custom functional blocks can be stored in the memory 1150 or media disc 1160.

XIII. Example Method of operating a Block-Based Processor

FIG. 12 is a flowchart 1200 outlining an example method of executing instructions using custom function blocks, as can be performed in certain examples of the disclosed technology. For example, the microarchitecture discussed above regarding FIG. 9 can be used to perform the method of FIG. 12, although the method is not limited exclusively to hardware implementing such a microarchitecture.

At process block 1210, execution of an instruction block having block-based ISA instructions is initiated. For example, an instruction block can be read from memory, stored in an instruction cache, and instruction block headers and/or instructions can begin being decoded.

At process block 1220, one of the instructions of the instruction block is executed. The executed instruction specifies use of a custom function block that is implemented with a configurable logic device. In some examples, the configurable logic device is a one-time, programmable device such as a PROM. In other examples, the configurable logic device can be reconfigured a number of times, for example, by electrically erasing the programming of the configurable logic device and applying a new programming to the device (e.g., as in an EEPROM or flash memory). In some examples, this reconfiguration can occur as a set of instruction blocks is being executed, while in other examples, operation of a block-based processor executing the program is stopped in order to be reconfigured, and then execution is later resumed.

At process block 1230, a target instruction indication is sent by the custom function block that executed the instruction at process block 1220.

At process block 1230, an instruction completion signal is sent by the custom function block that executed the instruction at process block 1220. This signal includes (or alternatively, can be used to obtain) the target instruction information. The target instruction indication indicates the instruction identifier and operand specifier for consuming the result and is sent to an instruction scheduler. In some examples, more than one target instruction is identified for consuming the result. In some examples, more than one result value is generated by the custom function block. The instruction scheduler can use this information to determine which additional instructions in the instruction block have their dependencies satisfied and can be designated as ready to issue. Because the custom function block is configured to produce a completion signal from which can be obtained target instruction information, instead of writing to a register to indicate satisfaction of dependencies, implementation of the instruction scheduler can be simplified and performance improved by reducing the complexity of the receiving instruction scheduler.

The target instruction indication indicates the validity and/or an instruction identifier for consuming the result and is sent to an instruction scheduler. The instruction scheduler can use this information to determine which additional instructions in the instruction block have their dependencies satisfied and can be designated as ready to issue. Because the custom function block is configured to send an instruction identifier instead of writing to a register to indicate satisfaction of dependencies, implementation of the instruction scheduler can be simplified and performance improved by reducing the complexity of the receiving instruction scheduler.

XIV. Example Method of Operating a Block-Based Processor with Optional Bypass

FIG. 13 is a flowchart 1300 outlining an example method of executing a set of two or more fused instructions with a block-based processor that includes one or more custom function blocks. For example, the microarchitecture discussed above regarding FIG. 10 can be used to implement the illustrated method, although other suitable microarchitectures can be used as well.

At process block 1310, the issue of a first instruction of a set of two or more fused instructions is delayed. For example, an instruction scheduler can detect an encoding of two or more fused instructions in an instruction block and delay issue of one or more of the fused instructions based on certain dependencies of the fused instructions. For example, issue of the first instruction can be delayed until all source operands for the fused instructions are available. In some examples, whether instructions are fused is indicated by an opcode encoded in the fused instructions. In other examples, the fusing of instructions is indicated by one or more bits encoded in the block header field. In still other examples, a special instruction in the instruction block is used to indicate that other instructions in the block are fused.

At process block 1320, it is determined that a second one of the fused instructions has its dependencies satisfied. For example, operands generated by other instructions in the instruction block can arrive at the operand buffer, values from memory load operations can be received, and/or register read operands can be received. In some examples, a compiler used to generate the block-based instructions arranges the instruction block to avoid deadlock and livelock situations that may arise with fused instructions.

At process block 1330, the first instruction, which was delayed at process block 1310, is issued. When issuing the delayed instruction, additional control signals can be generated to control the data path of the custom function block. For example, the control signals may indicate that one or more operands generated by the first delayed instruction can bypass the other operand buffer and immediately be consumed by another instruction that will issue immediately after the delayed first instruction.

At process block 1340, an operand buffer of a block-based processor can be bypassed for at least one source operand of an executing instruction. For example, based on control signals generated when issuing a delayed instruction, control hardware and the data path can be operated so as to select an operand from an execution unit of the data path, rather than reading an operand stored in an operand buffer.

At process block 1350, additional fused instructions in the set of fused instructions are executed. For example, a second instruction that receives a bypass operand can execute immediately after the first delayed instruction and consume a result generated by the first instruction as one or more of its source operands. In some examples, an instruction scheduler sequences instruction in the set of fused instructions to allow bypass of an operand buffer.

XV. Example Method of Configuring a Reconfigurable Logic Device

FIG. 14 is a flowchart 1400 outlining an example method of using a profiler to execute instruction blocks for a block-based processor. For example, the microarchitecture discussed above regarding FIGS. 2, 9, and 10 can be used to implement the method of FIG. 14, although other microarchitectures can also be adapted to the illustrated method.

At process block 1410, one or more instruction blocks are executed using general-purpose execution units of a block-based processor. As discussed above, such general-purpose execution units include integer ALUs, floating point ALUs, adders, multipliers, shifters, and other general-purpose execution units that are defined, at least in part, by the block-based processor ISA. Data can be gathered regarding execution of the instruction blocks as execution proceeds. In some examples, a block-based processor includes profiler registers that store data indicating, for example, the number of times particular instructions are executed, memory locations that are commonly accessed, sequences of operations that are commonly performed, and other suitable profile data. In some examples, software is used to capture all or a portion of the profiler data. For example, profiler variables can be compiled into an instruction block based on instrumentation inserted by a compiler or added by a programmer generating the instruction block code.

At process block 1420, based on performance data for the instructions blocks generated using a software and/or hardware based profiler, custom function blocks can be configured to perform functions from the instruction block. For example, if a series of operations not defined by the processor ISA are detected, these can be mapped to a custom function block. In some examples, specific functions not supported by the general-purpose execution units can be defined and mapped to the custom function block. The custom function blocks can be reconfigured to implement the new functions at different times, including prior to running the instruction block on the block-based processor, after running the instruction block a number of times, or dynamically as the program itself is running.

At process block 1430, the instruction blocks are executed using the newly configured custom function block that was reconfigured at process block 1420. In some examples, new instruction block code is also generated to implement the custom function, while in other examples, execution of the instruction block is automatically mapped to the custom function block. Thus, by using custom function blocks that can be configured at a suitable time, performance can be improved and energy consumption reduced through the use of custom function blocks. Use of a block-based processor architecture including the use of instruction identifiers generated by the custom function blocks to indicate completion and/or a destination for results generated by the custom function unit allow for efficient implementation of such custom functions rather than the use of general purpose registers as would be used in a RISC or CISC processor.

XVI. Example Method of Configuring Logic Devices with Custom Function Blocks

FIG. 15 is a flow chart 1500 outlining an example method of configuring a reconfigurable logic device, as can be performed in certain examples of the disclosed technology. For example, the FPGA discussed above regarding FIG. 3 can be configured to implement the block-based processor of FIG. 1 using the example microarchitectures discussed above regarding FIG. 2, 9, or 10, including custom function blocks discussed above.

At process block 1510, a description of block-based processor components is mapped to reconfigure logic device components of the FPGA. For example, a process designer can specify a description of the block-based processor in the hardware description language, such as SystemVerilog, SystemC, Verilog, or any other suitable combination of hardware description languages. In some examples, a description written in a traditional programming language such as C or C++ are used to describe at least a portion of the block-based processor. The description of the block-based processor can include any of the components discussed above. In some examples, the designer can specify specific FPGA cells to be targeted by elements of the processor microarchitecture. For example, the designer may specify that the instruction cache and/or the data cache are implemented using block RAM resources of the FPGA. In some examples, the programmer can use available macros provided by the FPGA vendor to implement custom function units, FIFO buffers, shift registers, and other components using economical mappings for that FPGA. In some examples, at least a portion of the custom function blocks are generated with using profiler data.

At process block 1520, a configuration bitstream is produced for implementing a circuit for the block-based processor that includes a custom function block that generates ready state data indexed by an instruction identifier. For example, a description of a block-based processor expressed in a hardware description language can be compiled to generate a netlist, and the netlist in turn used to generate a bitstream file. The signals indicated in the bitstream file can be applied to the configuration interface of an FPGA in order to configure the FPGA to perform functions for implementing a block-based processor according to the disclosed techniques.

At process block 1530, the reconfigurable logic device is configured using the bitstream generated at process block 1520. For example, some FPGAs have a configuration port that is used to serially stream data into configuration memory of the FPGA, thereby configuring the FPGA. In some examples, configuration memory of the FPGA is addressed through a parallel or other addressable port. In some examples, a configurable logic device having a structure similar to an FPGA can be configured once, but not reconfigured. In other examples, the FPGA can be electrically erased and rewritten to in order to provide a new configuration. In some examples, the FPGA is re-configured whenever the integrated circuit is re-powered, while in other examples, the FGPA configuration maintains state across repeated power cycles.

At process block 1540, the reconfigurable logic device is dynamically and partially reconfigured based on profiler data generated by executing instructions at process block 1530. For example, functions that consume a large portion of execution time of an instruction stream, or functions that exhibit a large amount of speedup when mapped to a custom function block, can be mapped to such blocks. Configuration information (e.g., a partial bitstream) is generated to program the updated processor, including information defining the custom function block function. The partial bitstream is applied to the configuration interface of the reconfigurable logic device, and execution of the instruction stream resumes. Thus, the modified circuit uses the newly-programmed custom function block to improve performance of the instruction stream.

XVII. Example Computing Environment

FIG. 16 illustrates a generalized example of a suitable computing environment 1600 in which described embodiments, techniques, and technologies, including configuring a block-based processor, can be implemented. For example, the computing environment 1600 can implement disclosed techniques for configuring a processor to implement disclosed block-based processor architectures and microarchitectures, and/or compile code into computer-executable instructions and/or configuration bitstreams for performing such operations including a custom function blocks, as described herein.

The computing environment 1600 is not intended to suggest any limitation as to scope of use or functionality of the technology, as the technology may be implemented in diverse general-purpose or special-purpose computing environments. For example, the disclosed technology may be implemented with other computer system configurations, including hand held devices, multi-processor systems, programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. The disclosed technology may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules (including executable instructions for block-based instruction blocks) may be located in both local and remote memory storage devices.

With reference to FIG. 16, the computing environment 1600 includes at least one block-based processing unit 1610 and memory 1620. In FIG. 16, this most basic configuration 1630 is included within a dashed line. The block-based processing unit 1610 executes computer-executable instructions and may be a real or a virtual processor. In a multi-processing system, multiple processing units execute computer-executable instructions to increase processing power and as such, multiple processors can be running simultaneously. The memory 1620 may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two. The memory 1620 stores software 1680, images, and video that can, for example, implement the technologies described herein. A computing environment may have additional features. For example, the computing environment 1600 includes storage 1640, one or more input device(s) 1650, one or more output device(s) 1660, and one or more communication connection(s) 1670. An interconnection mechanism (not shown) such as a bus, a controller, or a network, interconnects the components of the computing environment 1600. Typically, operating system software (not shown) provides an operating environment for other software executing in the computing environment 1600, and coordinates activities of the components of the computing environment 1600.

The storage 1640 may be removable or non-removable, and includes magnetic disks, magnetic tapes or cassettes, CD-ROMs, CD-RWs, DVDs, or any other medium which can be used to store information and that can be accessed within the computing environment 1600. The storage 1640 stores instructions for the software 1680, plugin data, and messages, which can be used to implement technologies described herein.

The input device(s) 1650 may be a touch input device, such as a keyboard, keypad, mouse, touch screen display, pen, or trackball, a voice input device, a scanning device, or another device, that provides input to the computing environment 1600. For audio, the input device(s) 1650 may be a sound card or similar device that accepts audio input in analog or digital form, or a CD-ROM reader that provides audio samples to the computing environment 1600. The output device(s) 1660 may be a display, printer, speaker, CD-writer, or another device that provides output from the computing environment 1600.

The communication connection(s) 1670 enable communication over a communication medium (e.g., a connecting network) to another computing entity. The communication medium conveys information such as computer-executable instructions, compressed graphics information, video, or other data in a modulated data signal. The communication connection(s) 1670 are not limited to wired connections (e.g., megabit or gigabit Ethernet, Infiniband, Fibre Channel over electrical or fiber optic connections) but also include wireless technologies (e.g., RF connections via Bluetooth, WiFi (IEEE 802.11a/b/n), WiMax, cellular, satellite, laser, infrared) and other suitable communication connections for providing a network connection for the disclosed methods. In a virtual host environment, the communication(s) connections can be a virtualized network connection provided by the virtual host.

Some embodiments of the disclosed methods can be performed using computer-executable instructions implementing all or a portion of the disclosed technology in a computing cloud 1690. For example, disclosed compilers and/or block-based-processor servers are located in the computing environment, or the disclosed compilers can be executed on servers located in the computing cloud 1690. In some examples, the disclosed compilers execute on traditional central processing units (e.g., RISC or CISC processors).

Computer-readable media are any available media that can be accessed within a computing environment 1600. By way of example, and not limitation, with the computing environment 1600, computer-readable media include memory 1620 and/or storage 1640. As should be readily understood, the term computer-readable storage media includes the media for data storage such as memory 1620 and storage 1640, and not transmission media such as modulated data signals.

XVIII. Additional Examples of the Disclosed Technology

Additional examples of the disclosed subject matter are discussed herein in accordance with the examples discussed above. For example, aspects of the block-based processors discussed above regarding FIGS. 1, 2, and 9 can be used to implement these additional examples, including FPGAs such as those discussed above regarding FIGS. 3 and 4.

In certain examples of the disclosed technology, all or a portion of a block-based processor are implemented by configuring an FPGA to include structures for executing programs expressed in the block-based processor ISA. In some examples, the processor is implemented in an embedded device such as for deploying in a network of Internet of Things (IoT). In some examples, structures such as caches, and storage used in the instruction scheduler, the load store queue and/or the register file are implemented in memories having a single write port or a single read port. In other examples, one or more of these structures are implemented in memories having multiple read and/or write ports. In some examples, an instruction block header, and one or more instructions of the instruction block can be fetched from memory and/or the instruction cache, concurrently. In some examples, a bypass mechanism allows for operations generated from the execution portion of the microarchitecture pipeline to bypass operands, thereby allowing for the back-to-back issue of instructions having a shared or chained dependencies. In some examples, the bypass mechanism allows for the avoidance of pipeline stall when there are more operands generated during an execution clock cycle than write ports on the instruction window operand buffer.

In some examples, the scheduler can use decoded or previously decoded instruction dependencies to wake up and issue instructions before they have been fetched. In some examples, storage for the instruction scheduler can be split in to two or more portions in order to map the storage to two or more physical storage units of an FPGA. In some examples, the instruction scheduler includes a parallel scheduler. In some examples, the scheduler is configured to refresh some but not all of an instructions ready state upon re-executing an instruction block. In some examples, the instruction scheduler includes an incremental scheduler.

In some examples of the disclosed technology, an apparatus includes a block-based processor having an instruction scheduler configured to issue at least one instruction and one or more custom function blocks configured to receive one or more input operands for the at least one instruction and generate an instruction completion signal indicating completion of a specific computation performed by the respective functional block. In some examples, the instruction completion data includes an instruction identifier indicating at least one instruction targeted by the at least one instruction. In some examples, the instruction completion data comprises an instruction identifier indicating a target instruction of the at least one instruction. In some examples, the scheduler issues a target instruction responsive to receiving the instruction completion signal, the instruction completion signal comprising an instruction identifier indicating the target instruction. In some examples, the custom function blocks are implemented with dynamically reconfigurable logic. In some examples, the custom function blocks are implemented with reconfigurable logic only prior to initiating processor operation. In some examples, the custom function block are implemented at least partially in custom logic.

In some examples, the custom function blocks can complete their respective computation in a variable number of clock cycles. In other examples, the custom function blocks complete their respective computation in a fixed number of clock cycles. In some examples, the block-based processor is configured to issue instructions out-of-order, and wherein the block-based processor is implemented using a field programmable gate array (FPGA). In some examples, the block-based processor includes at least two functional units including the custom function block, and the block-based processor is configured to issue two source operands to each of the at least two functional units concurrently, each of the two source operands being designated with the same source operand slot. In some examples of the disclosed technology, the instruction scheduler is a dynamically configurable scheduler. In other examples, function of the instruction scheduler is defined prior to processor runtime.

In some examples of the disclosed technology, a method of operating a configurable logic device to execute a block-based processor instruction set includes initiating execution of an instruction block containing a plurality of instructions encoded according to the block-based processor instruction set and executing one of the instructions, the executed instruction specifying use of a custom function block implemented with the configurable logic device. In some examples, the method further includes sending an identifier to an instruction scheduler, the identifier indicating a target instruction to receive a result generated by the custom function block. In some examples, the custom function block includes programmable logic devices of the configurable logic device, and the method further includes configuring the programmable logic devices to implement the custom function block. In some examples, the configuring occurs before the initiating execution of the instruction block. In some examples, the configurable logic device includes an operand buffer to store instruction operands, and the method further includes issuing a first instruction of a set of two or more fused instructions, the first instruction specifying use of the custom function block, and issuing a second instruction of the set of two or more fused instructions, the second instruction being issued in a sequence to allow bypass of an operand buffer.

In some examples, the method further includes delaying issue of a first instruction of a set of two or more fused instructions that has its dependencies satisfied, determining that a second instruction of the set of fused instructions has its dependencies satisfied, and issuing the delayed first instruction, the first instruction when executed, generating an operand consumed by the second instruction. In some examples, the method includes executing one or more instruction blocks with general-purpose execution units of the block-based processor; based on performance data for the instruction blocks generated by a profiler, configuring the custom function block to perform a function; and executing the instructions block with the configured custom function block.

In some examples of the method, a function performed by the custom function block is defined at least in part based on a parameter. In some examples, the parameter is defined by an operand of the executing instruction. In some examples, the parameter is defined by executing a different instruction than the executing instruction.

In some examples of the disclosed technology, a method of forming a block-based processor with a configurable logic device includes producing a configuration bitstream including configuration information for implementing a block-based processor with a configurable logic device, the block-based processor including an instruction scheduler configured to issue instructions, and a customizable function unit configured to perform operations specified by at least a portion of the issued instructions. In some examples, the method further includes, based on profiler data generated by the executing the instructions, dynamically, partially reconfiguring the reconfigurable logic device to improve performance of the instructions when executed with the block-based processor.

In some examples of the disclosed technology, the configuration bitstream is loaded by the processor on-demand as a result of executing a block that specifies a corresponding custom function block. In some examples, a dynamically-generated partial reconfiguration bitstream for the custom function block can reside in main memory or another memory accessible by the block-based processor, or in a computer-readable storage device or medium accessible by the block-based processor. In some examples, the computer-readable storage device or medium is accessed via a computer network. In some examples, the address of the bitstreams in memory are a function of the value of a field encoded a block header 520 that specifies that a particular custom function block is used by the associated instruction block.

In some examples, the method further includes storing the configuration bitstream in a computer-readable storage device or memory. In some examples, the method further includes applying the configuration bitstream to a configuration port of an integrated circuit comprising the configurable logic device, and executing the instructions with the block-based processor.

In view of the many possible embodiments to which the principles of the disclosed subject matter may be applied, it should be recognized that the illustrated embodiments are only preferred examples and should not be taken as limiting the scope of the claims to those preferred examples. Rather, the scope of the claimed subject matter is defined by the following claims. We therefore claim as our invention all that comes within the scope of these claims. 

We claim:
 1. A method of operating a configurable logic device to execute a block-based processor instruction set, the method comprising: initiating execution of an instruction block containing a plurality of instructions encoded according to the block-based processor instruction set; and executing one of the instructions, the executed instruction specifying use of a custom function block implemented with the configurable logic device, the configurable logic device including an operand buffer to store instruction operands, by: issuing a first instruction of a set of two or more fused instructions, the first instruction specifying use of the custom function block and producing at least one result operand, and responsive to data encoded in the first instruction or a second instruction, the data being encoded in a field exclusively used to indicate the second instruction is fused to the first instruction, issuing the second instruction of the set of two or more fused instructions to the custom function block after the first instruction executes, the second instruction being issued in a sequence so that the custom function block executing the second instruction will receive the at least one result operand by bypassing an operand buffer.
 2. The method of claim 1, wherein a function performed by the custom function block is defined at least in part based on a parameter.
 3. The method of claim 2, wherein the parameter is defined by an operand of the executing instruction.
 4. The method of claim 1, wherein the custom function block comprises programmable logic devices of the configurable logic device, the method further comprising: configuring the programmable logic devices to implement the custom function block.
 5. The method of claim 1, further comprising: executing one or more instruction blocks with general-purpose execution units of the block-based processor; based on performance data for the instruction blocks generated by a profiler, configuring the custom function block to perform a function; and executing the instructions block with the configured custom function block.
 6. A method of operating a reconfigurable logic device configured to execute an instruction set and having an operand buffer for temporarily storing instruction operands, the method comprising: receiving a first instruction having a first field exclusively used to indicate that the instruction is fused with a second instruction and having a second field indicating that the instruction is to be executed with a custom function block, and responsive to decoding the first field and the second field: issuing the first instruction for execution using the custom function block implemented with the reconfigurable logic device, producing at least one result operand; and issuing the second instruction to the custom function block for execution, the second instruction being issued in a sequence so that the custom function block executing the second instruction will receive the at least one result operand by bypassing an operand buffer.
 7. The method of claim 6, further comprising, based on the first field, executing the first instruction immediately before the second instruction.
 8. The method of claim 6, further comprising delaying the issuing the first instruction, despite all dependencies of the first instruction being satisfied, until all dependencies of the second instruction are satisfied.
 9. The method of claim 6, further comprising delaying the issuing the first instruction and the issuing the second instruction until all source operands for the first instruction and the second instruction are available.
 10. The method of claim 6, further comprising: executing the second instruction immediately after the first instruction, wherein at least one of the second instruction's source operands is generated by the first instruction.
 11. An apparatus comprising: a decoder to decode a set of two or more instructions and designate the set of instructions as fused when indicated by an opcode or another instruction in a group of instructions; a customizable function unit situated to perform operations specified by the fused set of two or more instructions; an operand buffer situated to temporarily store output operands produced by executing instructions with the customizable function unit and to output operands via a number of read ports; and an instruction scheduler configured to issue the fused set of instructions in a manner allowing bypass of the operand buffer, at least one of the fused set of instructions receiving a result produced by the executing instructions by bypassing an operand buffer.
 12. The apparatus of claim 11, wherein the instruction scheduler is further configured to, based on a field encoded in a first one of the fused set of instructions, execute the first instruction immediately before the second instruction, thereby allowing bypass of the operand buffer.
 13. The apparatus of claim 11, wherein the instruction scheduler is further configured to, based on the indication that the set of instructions is fused, delay issuing of a first instruction of the set of fused instructions until all dependencies of a second instruction of the set of fused instructions is satisfied.
 14. The apparatus of claim 11, wherein: the set of fused instructions comprises a first instruction and a second instruction; and the instruction scheduler is further configured to, based on the indication that the set of instructions is fused, execute the second instruction immediately after the first instruction, wherein at least one of the second instruction's source operands are generated by the first instruction.
 15. The apparatus of claim 11, wherein the instruction scheduler is further configured to: issue at least two of the fused instructions simultaneously, wherein the number of operands consumed by the simultaneously-issued fused instructions is greater than the number of read ports of the operand buffer.
 16. The apparatus of claim 11, wherein the opcode comprises data indicating which instructions in a stream of instructions are fused.
 17. A method comprising: producing a configuration bitstream comprising configuration data for implementing a processor with a reconfigurable logic device, the processor comprising: a decoder to decode a set of two or more instructions and designate the set of instructions as fused when indicated by an opcode or another instruction in a group of instructions; a customizable function unit situated to perform operations specified by the fused set of two or more instructions; an operand buffer situated to temporarily store output operands produced by executing instructions with the customizable function unit; and an instruction scheduler configured to issue the fused set of instructions in a manner that, when a first instruction of the fused set of instructions produces at least one result operand, the customizable function unit will receive the at least one result operand by bypassing the operand buffer.
 18. The method of claim 17, wherein the instruction scheduler issues at least two of the fused instructions simultaneously.
 19. The method of claim 18, wherein the number of operands consumed by the simultaneously-issued instructions is greater than the number of read ports of the operand buffer.
 20. The method of claim 17, further comprising: storing the configuration bitstream in a computer-readable storage device or memory. 